The effect of free electrons on ionization chamber saturation curves.

The effect of the collection of free electrons--those which have not formed negative ions in the gas of a parallel-plate ionization chamber--is considered for the case of continuous radiation. A theory and its solution, valid for the entire voltage range, is given. The solution is based upon the saturation theory of Townsend, and free electrons are included in a perturbative fashion. The collection of free electrons becomes important at exposure rates above 430 R/min. Since the electron contribution involves an extra dependence on exposure rate, some of the wide variation in the cavity gas parameter (m value) reported in the literature may be due to the presence of free electrons.